In recent years, as a driving assistance technique applied to vehicles such as cars, an imaging device such as a CCD camera has been mounted on a vehicle to capture an image of the surrounding of the vehicle as a visible image. In such driving assistance technique, first, information on a subject requiring driving assistance, for example, a pedestrian, a traffic light and the like around the vehicle, is generated by processing the visible image captured by the imaging device, and driving assistance corresponding to the state surrounding the vehicle is performed based on the information thus generated.
However, the state of the pedestrian walking around the vehicle, such as the number of persons, body build, posture, carried items, and moving direction, varies each time the visible image around the vehicle is captured. Further, when the driving state of the vehicle, such as the turning direction of the vehicle and the attribute of a road on which the vehicle is running, varies, shape and size of the pedestrian and even the traffic light installed on the road in the visible image around the vehicle also vary. As a result, in an aspect of detecting the object necessary for driving assistance from the visible image of an imaging object including the object, driving assistance lacks precision. Thus, in the above-mentioned driving assistance technique, there is a demand for a technique for improving the detecting accuracy of the object in order to improve the accuracy of the driving assistance.
Among techniques for distinguishing an object based on its optical characteristics, patent document 1 describes a known technique using a hyper spectrum sensor as the spectrum measuring apparatus mounted on an artificial satellite for use in soil investigation on the earth. The hyper spectrum sensor described in patent document 1, for example, detects a spectrum so that light from the object is dispersed into components according to each wavelength and optical intensity at each wavelength is associated with the wavelength. In other words, a continuous spectrum with respect to wavelength is handled as the optical characteristics of the object. FIG. 10 is a diagram showing an example of the optical structure of a hyper spectrum sensor serving as such spectrum measuring apparatus.
As shown in FIG. 10, an inlet 111, a mirror 112, a condenser 113, a shielding plate 114, a collimator 115, a spectroscope 116, an imager 117 and a measuring unit 118 are arranged in this order in a hyper spectrum sensor 100 along a light traveling direction. Each element of the hyper spectrum sensor 100 is configured so that optical characteristics are continuous in one direction intersecting a hypothetical light beam representing a light flux that passes the elements, that is, an optical axis (extending in a lateral direction in FIG. 10). In the hyper spectrum sensor 100 having such structure, partial sunlight reflected on an object 120, which is a ground surface serving as a measured object, first enters the apparatus through the inlet 111 and is guided to the condenser 113 by a reflecting action of the mirror 112. The light incident on the condenser 113 is condensed by a condensing action of the condenser 113 toward the shielding plate 114, and only light toward a single slit 114a is guided to the collimator 115 by a shielding action of the shielding plate 114. The light passed through the single slit 114a in this manner is guided to the spectroscope 116 as collimated light by an optical action of the collimator 115 and each parallel beam is dispersed into wavelength components by a spectral action of the spectroscope 116. The wavelength components dispersed by the spectroscope 116 (wavelength component λa to wavelength component λb) are image-formed on regions of the measuring unit 118, which are divided according to wavelength, for example, light receiving elements 118a, 118b of a CCD image sensor or a CMOS image sensor, by an image-forming action of the imager 117.
In such hyper spectrum sensor 100, the spectrum of only the light passed through the single slit 114a of the light condensed by the condenser 113 is measured. In other words, in the light from the object 120 as the ground surface, only the light from a linear measuring part 120a in a direction in which the optical characteristics are continuous in the single slit 114a, that is, a longitudinal direction Dm of the single slit 114a, is extracted by the single slit 114a. Then, only optical information on the linear measuring part 120a is input to the hyper spectrum sensor 100 each time. Thus, in the hyper spectrum sensor 100, by repeating spectrum measurement of the one-dimensional measuring part 120a along a flight direction of the artificial satellite, the optical characteristics of the object 120, which is a two-dimensional ground surface, are measured.